I had the Mamiya m645 for all of 2 weeks before selling it and buying an rb67. In that time I only shot one roll - some expired portra 160 nc that I found in the camera after i bought it. On top of that I absolutely botched the development, making a good 8 or so shots completely unusable. But despite that, I am very impressed with the camera. These photos were taken around my house when I first got the camera with the Mamiya 55mm 2.8 sekor c lens.
Sort of an intermediate level between 35mm and more serious medium format cameras, the m645 is both familiar and alien compared to cameras like my Nikon f3 and other slr's. The controls are similar and it is a very easy camera to get the hang of, but in practice it feels much more like its larger counterparts. Although it isn't fully mechanical, it feels pretty close. Winding, settings, and focus are all manual(unless you use the AE prism), and while the inclusion of an electronic shutter is disappointing, it is otherwise all manual. I didn't really get to use this camera enough to feel too many of the nuances, but what i will say is that it was very awkward to use with the prism finder. There is no good way to grip the body, and the shutter button is positioned awkwardly my best piece of advice if you decide to get this camera is to get the hand grip as well, especially for use with the prism finder. Even with the waist level finder it will be helpful though.